Is there a noticeable difference in the calorie-burning benefits of road vs. off-road cycling?

Question

I monitor my rides using FitBit and Strava. I started out as a full-time road cyclist. However, I've recently begun gravel cycling. My primary purpose for cycling is fitness, in addition to enjoyment, fresh air, and exploration.

I've noticed that when I ride on dirt trails, I still feel like I am getting a great workout, but according to FitBit/Strava trackers, I expend less effort on trails. My hypothesis is that this is the case due to the rough terrain slowing me down, time spent having to navigate obstacles, etc... However, I do end up going up some of the toughest hills I've ever gone up on dirt, just not quite with the same level of momentum as I would on the road. I also know some friends who lost over 100 lbs strictly mountain biking.

So my question is, based on your knowledge, experience, and/or research, is there generally a significant calorie-burning difference between road and off-road cycling for a given time period?

What I mean by "for a given time period" is that, if I were to gravel cycle off-road for 2 hours versus ride on road for 2 hours, should I expect to generally burn less calories?

I add that constraint because obviously, if I were to gravel cycle off-road for 4 hours, I would likely burn more than if I road cycled for 2 hours. I'll add the caveat that cycling off-road opens up my opportunities and interests, so I may cycle for 1-2 more days than I would if I were limited to road-only, so even this comparison is not absolute in terms of overall fitness.

Answer 1

All that a smartphone app or cycle computer may hope to achieve, is to provide an estimate of the burnt calories. They do this by taking your speed, and possibly climb rate, and some assumptions about you and your bike to derive the likely physical effort required to maintain this speed/climb rate.

• If you have not told your app how heavy you + bike are, they cannot give a correct estimate for climbing.

• The device has no information on current wind or your drag coefficient, so your app cannot give a correct estimate for air drag.

• The device does not know the bumpiness of the path, nor does it know what kind of shock absorbers are built into your suspension (if the bike has suspension), and thus the rolling resistance cannot be estimated at all.

In your case, the app does not know the difference between your two bikes, nor the difference between the two road surfaces. As such, it will use the same assumptions in both cases.

Since your mountain bike has a) a suspension that includes shock absorbers, b) much lower tire pressure, and c) is ridden on much less smooth paths, the effective rolling resistance of the mountain bike is significantly higher, and the app does not know this. As such, it will underestimate your effort.

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If the device can monitor your heart rate, it might be a little more precise, but it's still a rough estimate. The only source for precise measurement would be a power meter that directly measures the force and rotation speed you apply to your cranks.

Answer 2

Off-road a few maximum power bursts up a steep incline will feel exhausting, but don’t burn a lot of calories because the duration is so short. Usually you also have a lot of descents, technical sections etc. where the power output is low.

Technical sections might feel exhausting because of all the core and arm strength required but overall the energy expenditure is not that high. The leg muscles are just so much bigger and can output so much more power.

You also tend to feel hotter and sweatier because the speed tends to be lower, so you have less wind chill and less evaporation.

Of course a lot of this depends on the terrain and intensity.

With a road bike it’s pretty easy to spend 2 hours at a certain power output. On a good route you never really have to slow down or stop pedaling.

Even interval training on the road doesn’t burn that many calories. If you spend half the time at 300W and the other at 100W (recovering) the average is still just 200W but will feel quite exhausting.

I feel like the best way to burn as many calories as possible within a certain time frame is to pick and maintain a power output you can sustain for the whole duration. Humans have very good endurance and very bad high power, anaerobic strength.

You’d need a power meter for accurate numbers. Off-road even the power meter could be slightly inaccurate because it can’t measure what you are doing with your core and upper body muscles (e.g. jumping over obstacles).

I think calorie estimates soley based on velocity, elevation change and rider+bike weight will be even more inaccurate off-road. They can’t account for muddy sections, can’t account for tyre pressure, can’t account for whether your suspension was locked or not etc. etc. On-road the biggest source of inaccuracy is wind speed and wind direction.